A. Field of the Invention
The present invention relates generally to a manual focusing circuit using a signal stabilizer, and more particularly to a manual focusing circuit using a signal stabilizer in an inner focus lens, which can prevent destabilization caused by noise when a user focuses manually.
B. Description of Related Art
Conventional focusing methods of a camera include a manual focusing method and an automatic focusing method. In the manual focusing method, focus is made by a signal produced from a manual focusing circuit when a user manually rotates a rotation ring.
Reference will now be made to a conventional manual focusing circuit with reference to the accompanying drawings. FIG. 1 is a detailed circuit diagram illustrating the conventional manual focusing circuit.
The conventional manual focusing circuit includes a power supply VCC for activating a circuit, a manual ring 80 having a projection, a first photoelectric conversion element 40 connected to the projection of the manual ring 80 and positioned to make a phase difference of an output signal ninety degrees, a second photoelectric conversion element 60, resistors 50 and 70 for producing pulse signals S90 and S100 produced from the first and second photoelectric conversion elements 40 and 60, and a D flip-flop 120 for receiving the pulse signals S90 and S100 produced from the resistors 50 and 70 producing a pulse output signal S110, that is, a rotation direction signal.
The operation of the conventional manual focusing circuit is as follows:
When the operation is started, power is supplied to the light emitting diodes 40D and 60D of the first and second photoelectric elements 40 and 60, to emit light.
When the user manually rotates the manual ring 80, the light from the light emitting diodes 40D and 60D travels through the first and second photoelectric elements 40 and 60, respectively, or is blocked by a projection of the manual ring 80, and the pulse signals S90 and S100 produced through resistors 50 and 70 are electrically turned ON or OFF. An operational waveform for this is illustrated in FIG. 2.
Referring to FIGS. 2 and 3, the pulse signals S90 and S100 includes a noise caused by a mutual interference between the two signals S90 and S100. The pulse signal S100 is inputted to a clock terminal CLK of the D flip-flop 120 and a pulse signal S110 is produced through the D flip-flop 120. The operational waveform chart for pulse signals S90, S100, and S110 is illustrated in FIG. 2. A microcontroller (not shown) obtains a rotation number by counting a pulse number of the pulse signal S100 for a predetermined time.
However, when the noise from pulse signal S100 greatly affects the output signal S110 in the conventional manual focusing circuit, it causes an increase in the pulse number. As a result, the pulse number of pulse signal S100 cannot be accurately counted. In addition, since the output from the D flip-flop 120, that is, a rotation direction signal S110, is produced as a high or low signal with noise, an accurate direction cannot be determined.
To overcome these disadvantages, an integrated circuit having low noise is used. However, due to the size of the noise, malfunctions occasionally occur with a hysteresis width of the low noise integrated circuit.
Another disadvantage of the conventional manual focusing circuit is that a great deal of power is consumed since a dry batter is used as the power supply and the power is continuously supplied to the photoelectric conversion element.